25% Dot Gain on Press Sheet

[Lukas Engqvist]

I suspect printing order to be KCMY, and seems K is lowest dot gain could this be due to fount solution, where paper getts damper and dotgain increases?
Some tests would be to switch colour and see if it is the unit that is causing the dot gain. If it follows the colour and not the unit, then it is to do with the ink. If if follows the unit, then you can eliminate the ink and focus on mechanical or wetness issues.
One thing that might be good to eliminate is also the paper, if you have a sword you can measure it, but also try another stock (trying other paper is usually the first we eliminate, because it just means taking a couple sheets )
And as mentioned the packing, and the blankets…*man RErint was just so to teh point :P I now see some have said similar things, but just remember one thing at a time and keep a log so you know what change did what

[gordo]

Let's assume that you've checked the plates and on all 4 plates the 40% tone patch reads 40%

You are running your C and M at almost the same density (1.35 and 1.40) yet the M has twice the gain of the C. You would expect them to have almost the same dot gain with M being very slightly higher than C.
The K is running at the highest density (1.80) but has the lowest gain (15%) - the opposite of what you would expect.
The Y is running at the lowest density yet has the highest dot gain - again, the opposite of what you would expect.

You've gotten some good advice in this thread but things are very messed up.
Is your presswork currently matching your proofing?
If so, perhaps you should monitor dot gains and SIDs of your live presswork to see if these numbers remain consistent on live work.
Are you running a KCMY sequence or a KMCY sequence since M ahead of C will skew color to the red side.

Try having your press cleaned and put magenta in all 4 units. They should all print the same. Same dot gains at the same densities. Even the press operator would understand that. If they don't then that might reveal a mechanical press problem with one or more units. If you can afford it - do the same with the Y ink (i.e. Y ink in all 4 units) and with the K ink (i.e. K ink in all 4 units).

Buy a USB microscope so that you can take photos of the dots and solids to see how they are performing. Do a search for USB microscope on eBay and you'll see plenty (like this one: USB 20X~ 200X Digital Microscope 1.3MP Video Camera New | eBay ) for less than $50. Every shop should have one (mine's 20x/200x).

best, gordo

[David Milisock]

I'm being told by the pressman that densities are to spec, blankets and packing are to spec
as well.

Thx David

Ok then what are the ink densities?

[gordo]

Ok then what are the ink densities?

You may have missed that info in this thread. The densities are: C 135, M 140, Y 100, K 180.

best, gordo

[David Milisock]

You may have missed that info in this thread. The densities are: C 135, M 140, Y 100, K 180.

best, gordo

Thanks I did miss them. They don't seem too hot (the yellow may be a bit up) but what does the ink manufacture recommend?
It appears that the media curve for this device is faulty.

[TerryWyse]

Sorry Ti7, ALL colors are gaining C+17, M+25, Y+25, K+15.

Those numbers are seriously out-of-balance (and likely out-of-GRAY balance!).

Other than mechanical issues such as slur, they should be checking blanket packing and all manner of "pressures" that could cause as well as ink/water/chemistry issues. It could seriously be almost anything causing this problem. You should also check what ink densities they were running when they arrived at those numbers. Running a too-low ink density with cyan and black and/or too-high solid ink densities with yellow and magenta could cause that sort of imbalance.

It's the *imbalance* of those TVI values that concerns me the most, not the absolute values you're getting.

Regards,
Terry

[Lukas Engqvist]

Sorry for just adding short notes as I think of them.

One very important thing with a calibration sheet is that there is the temptation to run too few copies and then judge the press condition before the press is running at normal speed and in normal conditions. It is more of a reminder than what will solve the issue at hand. What triggered this was the discussion about make ready sheets.

[meddington]

One very important thing with a calibration sheet is that there is the temptation to run too few copies and then judge the press condition before the press is running at normal speed and in normal conditions. It is more of a reminder than what will solve the issue at hand. What triggered this was the discussion about make ready sheets.

A very good point by Lukas...
Press calibration runs should be long enough for the process to stabilize, and sampling of sheets taken for averaging. Most of the responses thus far likely presume this is the case.